The invention pertains generally to the field of semiconductor, nonvolatile memories, and, more particularly, to the field of vertically-integrated, flash EEPROMS which can be manufactured with sufficient density to be cheap enough to compete with rotating magnetic media for bulk memory applications. The vertically-integrated, flash EEPROM according to the teachings of the invention is especially useful in personal computers of the laptop, notebook and palmtop variety although it is broadly applicable to any application where large, nonvolatile memory is needed which is physically rugged and competitive with disk drives in price.
Flash EEPROMS are known in the prior art, but the problem to date has been that they cannot be made cheaply enough for them to have mass market appeal. The size of prior art EEPROM cells has been so large, that the number of cells per semiconductor die that can be made with adequate yield was too low to have a cost which was competitive with rotating memories such as disk drives.
Prior art flash EEPROM cells of the most aggressive design made by Intel Corporation of Santa Clara, Calif. are 78 square microns using 0.8 micron design rules. With a semiconductor die size of 1 square centimeter, this cell size allows flash EEPROMS of 48 megabits to be built for a cost of about $30 per megabit.
In contrast, small disk drives can be manufactured for about $5 per megabyte. Therefore, a need has arisen for a smaller flash EEPROM cell such that more dense memories can be built for lower cost.